1. Field of the Invention
This invention relates to a device for conveying and discharging bulk material such as bark mulch or any granular or pulverized material.
2. State of the Art
There are a number of conveying devices suitable for granular or pulverized material which utilize screw conveyors and rotary valves. None, however, are particularly suited for conveying and discharging bark mulch. Bark mulch is defined as a mixture of organic and/or inorganic materials usually comprised largely of plant and wood residues, which is generally composted and processed and is used mostly in the agricultural industry as a soil amendment, a ground cover for erosion and weed control, or for decorative purposes in landscaping. The known designs are all subject to jamming due to the build-up of bark mulch which tends to clump together and move as a large mass, instead of being easily shearable and moving as individual particles.
"Bulk Feed Body" is disclosed in Hoffstetter, U.S. Pat. No. 2,939,592, in which a screw conveyor feeds an inlet to a rotary valve. This device is primarily designed for grain or dry loose material. The apparatus utilizes a single screw conveyor which would move material such as bark mulch, but would result in compartmental bridging. The consequent build-up of the bulk material could rupture the end wall. Wolford, U.S. Pat. No. 3,443,763, also discloses a bulk feed apparatus in which a screw conveyor feeds an inlet to a rotary dispensing head. Likewise, the Wolford apparatus discloses a single screw conveyor used for displacing grain, salt and other free-flowing material. Similar problems in terms of build-up of material exist with this apparatus when utilized for moving materials such as bark mulch. The Wolford apparatus employs a material handling dispensing head and basically slings or throws the feed material by centrifugal force.
Temple, U.S. Pat. No. 2,757,049, for a "Flour Valve." It uses a helix in a rotation away from the helix angle in order to vent air into the feed. This system is also particularly adapted to freeflowing feed material.
Hickey, et al., U.S. Pat. No. 3,263,592, discloses an "Apparatus for Processing Fat-Containing Solids" which is not adaptable to discharging bulk materials. The Hickey machine discloses a single screw conveyor having the disadvantages discussed above.
"An Unloading System for Bulk Material Bins," Nadolske, U.S. Pat. No. 3,270,921, uses a moving air lock for displacing grains. The Nadolske apparatus includes a moving air lock with rubber tipped vanes. The apparatus disclosed in Nadolske would be prone to continuous jamming if utilized to displace bark mulch, as the long fibrous nature of the material tends to fold the airlock seals back and material bridges in the hoppers.
Burinsky, U.S. Pat. No. 3,314,596, for a "Forage Blower" discloses the use of an angled knife in conjunction with straight vanes on a fan along with a single screw conveyor. The knife is positioned on the outlet side of the fan. The disadvantages of the single screw conveyor have been discussed previously. The Burinsky apparatus would not be capable of conveying material because this type of fan will not build air pressure if a large portion of material plugs the fan inlet or outlet. This is a high speed application as opposed to a low speed heavy torque apparatus as disclosed in the present invention. Furthermore, the fan utilized in this apparatus is extremely noisy, and when handling bark mulch, a very high strength fan would be required.
Vinyard, U.S. Pat. No. 3,348,652, discloses the use of a converging screw conveyor system, but unlike the present invention, it gathers randomly spaced debris with the conveyor and seldom, if ever, running at full capacity due to the design of the conveyor housing.
Johnson, U.S. Pat. No. 3,926,377, is an apparatus for moving granulated and pulverized material. The feed drops through an air lock. The apparatus is not suited for conveying fibrous materials. Fibrous materials tend to jam the airlock and plug the distributor disks.
Boyhont, U.S. Pat. NO. 4,109,966, discloses a pneumatic conveying device which utilizes a single screw press to dewater pulp type material. Stringy material such as bark mulch would plug up the inlet and outlet of the chamber of the Boyhont device.
Oury, U.S. Pat. No. 4,117,920, discloses a converging single pitch screw conveyor. The "Auger Hopper" disclosed in Oury has no means to meter material other than the size of the outlet opening in the trough.
Machnee, U.S. Pat. No. 4,432,675, for a "Pneumatic Feed Control for Pneumatic Seeder and the Like" shows an air seeder which is not suited for displacing bark mulch because the shear points would tend to jam up. Small orifices would plug and this type of fan, like that used in the Burinsky devise, would lose air pressure.
Hellerman, U.S. Pat. No. 4,486,126, a "Pneumatic Conveyor for Silage and Haylage" is a variation of the Burinsky patent which discloses rotary cutting knives which counter-rotate to the airlock vanes. The knifes move the material back into the gravity feed system and act as wipers rather than shear points. Tenacious fibers as in bark mulch would jam, require high power and large vanes to handle induced stresses.
Schumacher, U.S. Pat. No. 4,617,177, shows a screw to dewater raw materials and is not at all related to the present application. A German patent, Patent No. 374033, also shows the state of the art of devices used for conveying materials.